1. Field of the Invention
The present invention relates to a head cleaning method and device for a thermal printer, and a recording sheet roll for the same. More particularly, the present invention relates to a head cleaning method and device for a thermal printer, and a recording sheet roll for the same, with which a thermal head can be cleaned with good efficiency.
2. Description Related to the Prior Art
There is a thermal printer in which heating elements of a thermal head is pressed against a recording surface of a thermosensitive recording sheet. An image is recorded by color development of the recording sheet. An example of the recording sheet is continuous, and is wound in a form of a recording sheet roll to be loaded in the thermal printer. After the image recording, a cutter in the thermal printer cuts the continuous recording sheet to obtain a print sheet with an image.
A front edge of the recording sheet roll in an unused state is likely to have an unwanted curvature, has an inclination to a direction perpendicular to lateral edges, or other features with low quality. A known model of the thermal printer is constructed to execute a precutting process, in which the front edge of the recording sheet roll is cut neatly upon newly setting the recording sheet roll in the thermal printer. In the precutting process, the continuous recording sheet is drawn from the recording sheet roll. A portion having the front edge is cut away at a predetermined precutting length, and is removed and ejected from the thermal printer. The precutting process, for example, is effected upon detection of closing of a lid for a roll loading chamber after the recording sheet roll is set in the roll loading chamber.
It is likely that dirt, dust or the like sticks to the heating element array of the thermal head. The dirt may have been stuck on the recording sheet. The dust may be particles created from a protective layer in the recording sheet. The thermal head must be cleaned periodically because dirt of the thermal head will influence the printing quality. To clean the thermal head, there is a cleaning sheet roll for maintenance as accessory to the recording sheet roll. The cleaning sheet roll is a roll of a continuous cleaning sheet having an abrasion layer, and has appearance similar to that of the recording sheet roll. The cleaning sheet roll is set in the thermal printer for cleaning operation instead of the recording sheet roll.
When a cleaning command signal is input with the cleaning sheet roll set in the thermal printer, the continuous cleaning sheet is drawn from the cleaning sheet roll, and fed to a position between the thermal head and a platen roller. When a portion of the cleaning sheet with a predetermined length is passed between the thermal head and the platen roller, the cleaning sheet is stopped in a temporary manner. One of the thermal head and the platen roller is moved to the remainder to squeeze the cleaning sheet. The cleaning sheet starts again being fed. The abrasion layer is rubbed on the heating elements to wipe away dirt or dust from those. The cleaning sheet having rubbed the thermal head is cut by the cutter in the same manner as the recording sheet, and is ejected from the thermal printer.
As the thermal printer executes the precutting process automatically, a front portion of the cleaning sheet is automatically precut upon setting of the cleaning sheet roll. This is a wasteful operation, because the precutting process is irrespective of the unused state of the front portion of the cleaning sheet, and discards the front portion in vain. Also, a user is likely to mistake the precutting process for a cleaning process, and remove the cleaning sheet roll without using the cleaning sheet roll for cleaning the thermal head.